Add the `autolabels` job to common-ci-tasks

Add the https://gitlab.com/fforster/autolabels/ job to common-ci-tasks.

• Create the gitlab-com/gl-infra/autolabels repository
• Migrate the code to the newly created repository.
• Add a common_ci_tasks.autolabels option to the GitLab project Terraform module at https://ops.gitlab.net/gitlab-com/gl-infra/terraform-modules/gitlab/project/
• Decide whether to move the CI task definition from the autolabels repository to the common-ci-tasks repo.
• Add the autolabels job to the common-ci-tasks repo.
• Generate autolabels PrATs for projects managed by infra-mgmt by default.
  • gitlab-com/gl-infra/infra-mgmt!1483
  • gitlab-com/gl-infra/infra-mgmt!1484
• Add autolabels to the standard template (templates/standard.yml).